661571691 has 16 divisors (see below), whose sum is σ = 971284608. Its totient is φ = 397203200.

The previous prime is 661571663. The next prime is 661571723. The reversal of 661571691 is 196175166.

It is a cyclic number.

It is not a de Polignac number, because 661571691 - 2¹³ = 661563499 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661571191) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 90150 + ... + 97211.

It is an arithmetic number, because the mean of its divisors is an integer number (60705288).

Almost surely, 2^661571691 is an apocalyptic number.

661571691 is a deficient number, since it is larger than the sum of its proper divisors (309712917).

661571691 is a wasteful number, since it uses less digits than its factorization.

661571691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 187482.

The product of its digits is 68040, while the sum is 42.

The square root of 661571691 is about 25721.0359628068. The cubic root of 661571691 is about 871.3493356668.

The spelling of 661571691 in words is "six hundred sixty-one million, five hundred seventy-one thousand, six hundred ninety-one".